1. Field of the Invention
This invention relates generally to a method of coating a conductive polymer on a substrate and to materials produced thereby. In particular, the present invention relates to a method of coating a conductive polymer on selected areas of a substrate in a controlled pattern by first inhibiting the formation of the coating on certain areas of the substrate and then applying a conductive polymer coating to the non-inhibited areas.
2. Description of the Prior Art
The impartation of increased electrical conductivity to substrates such as textile fabrics is well known. Textiles, such as fibers, yarns, and fabric, having a conductive polymer coating, are disclosed by Kuhn, et al. in U.S. Pat. No. 4,803,096. These textiles, while finding application in the control of static electricity, attenuation of electromagnetic energy, and resistance heating, are generally isotropic, which may impose limitations on their use.
Methods have been suggested to increase the electrical conductivity of only a portion of a substrate. For instance, Pittman, et al., U.S. Pat. No. 5,102,727 discloses textiles having a conductivity gradient produced by blending conductive and non-conductive yarns. Likewise Gregory et al., U.S. Pat. No. 5,162,135 teaches a conductive gradient achieved by contacting a conductive textile with a chemical reducing agent. These two methods are believed to be acceptable for producing conductivity gradients in simple patterns but difficult to apply in the production of more complex patterns.
Other methods have been disclosed in which an entire substrate is coated with a conductive polymer and then selected portions of the conductive polymer are removed. Adams, Jr. et al., U.S. Pat. No. 5,292,573 for instance teaches a method in which a textile fabric coated with a conductive polymer is subjected to a water jet process which removes a portion of the coating from selected areas of the substrate. Since only a portion of the coating is removed by the water jet, the difference in conductivity between different areas that can be achieved may be limited. Further, the process is inherently limited by the expense and sophistication of the water jet equipment required to practice it.
DeAngelis et al., U.S. Pat. No. 5,624,736, teaches a method in which selected areas of a substrate, already having been coated with a conductive polymer across its whole surface, are further coated with a protective film. The substrate is then subjected to a third treatment in which a chemical etching agent is used to remove the conductive polymer from the exposed portions of the substrate which were not coated with the protective film. Finally the substrate is rinsed to remove excess etching agent. Such a process, with so many operational steps, is rather complicated and lengthy and, like any process which involves coating an entire substrate only to remove large portions of the coating, necessarily involves a good deal of material loss.
For these reasons, there still exists a need for a simpler, quicker, and less wasteful method of coating substrates with conductive polymers in which only selected areas are coated in the first: instance and which is readily adaptable to producing complex patterns of varying conductivity on large substrates.